2020牛客暑期多校第一场J题

牛客多校暑期第一场J题：

题目：
AC代码：

using namespace std;
typedef long long ll;
const int MOD = 998244353;
ll inv[2000001];
void pre(int MOD){ 
    inv[0] = inv[1]=1; 
    for(int i = 2; i < 2000001; i++)
        inv[i] = ((MOD - MOD / i) * inv[MOD % i]) % MOD; 
}  
 
long long quick_pow(long long n, long long p, long long k){
    long long ans = 1;
    while(p){
        if(p & 1) ans = (ans % k * n % k) % k;
        p >>= 1;
        n = (n % k * n % k) % k;
    }
    return ans % k;
}
ll xxx[2000001];
void solve(){
    ll temp = 1;
    for(int i = 1; i <= 2000000; i++){
        temp = temp * i % MOD;
        xxx[i] = temp;
    }
}
int main(){
    solve();
    ll n;
    while(~scanf("%lld", &n)){ 
        ll fenzi = 1;
        ll fenmu = 1;
        fenmu = xxx[2 * n + 1];
        fenzi = xxx[n] * xxx[n] % MOD;
        cout <<  quick_pow(fenmu, MOD - 2, MOD) * fenzi % MOD << endl;
    }
    return 0;
}